Chapter 08 Environmental Health and Toxicology
Outline • Environmental Health • Infectious and Emergent Diseases • Antibiotics and Pesticide Resistance • Toxicology • Movement, Distribution, and Fate of Toxins • Minimizing Toxic Effects • Measuring Toxicity • Risk Assessment • Establishing Health Policy
Environmental Health • Health - a state of complete physical, mental, and social well-being • Disease - an abnormal change in the body’s condition that impairs physical or psychological function • Diet and nutrition, infectious agents, toxic chemicals, genetics, trauma and psychological stress all play roles in morbidity (illness) and mortality (death).
Global Disease Burden • Life expectancy increases as infant mortality decreases. • Disability-adjusted life years (DALYs) - combine premature deaths and loss of healthy life resulting from illness or disability • Chronic conditions account for 60% of premature deaths and 50% of diseases. • By 2020, heart disease may become leading source of disability and disease worldwide. Global cancer rates will increase by 50%.
Global Disease Burden • Diabetes is on the increase. One-third of children born in North America today will develop diabetes in their lifetime due to poor diet and little exercise. • WHO projects that psychological conditions could increase their share of the global disease burden from 10% currently to 15%. • Depression will be the second largest cause of all years lived with disability. • Tobacco related lung diseases are increasing. Biggest single cause of death worldwide.
Infectious Diseases • Communicable diseases are still responsible for about 1/3 of all disease-related deaths. • Majority in countries with poor nutrition, sanitation, and vaccination • Malaria is a major disease in tropical areas. Two million people die each year. • Better nutrition, clean water, improved sanitation and inoculation of children could eliminate most of the deaths.
Pathogens • Pathogens are disease-causing organisms. They include: • Viruses • Bacteria • Protozoans • Parasitic worms • Flukes • Greatest loss of life in a single year from a pathogen was in 1918 when the flu epidemic killed 50 to 100 million people worldwide. Today we are concerned that bird flu (H5N1) might cause an even larger outbreak.
Elephantiasis – caused by parasitic worm (& sometimes persistent volcanic ash exposure) At any given time, about 2 billion people suffer from worms, protozoans, and other internal parasites.
Emergent Diseases • An emergent disease is one never known before, or one which has been absent for at least 20 years. • Growing human populations push into remote areas where they encounter pathogens. • Air travel makes it possible to spread emergent diseases around the globe quickly. • West Nile virus was introduced into North America in 1999, and is now found everywhere in the lower 48 states.
Emergent Diseases • Cholera in Latin America • Yellow Fever in Kenya • Vibrio cholerae O139 in Asia • E. coli O157:H7 in South Africa and Swaziland • Rift Valley Fever in Egypt • Multidrug-resistant Shigella dysenteriae in Burundi • Dengue in Costa Rica • Diphtheria in Russia • Avian virus
Recent Disease Outbreaks • Hanta virus – US, rodent contact, frequently fatal, hemorrhagic • Dengue fever – virus, mosquito, 4 variants, mild form measle like, severe hemorrhagic • Buruli ulcer – Africa, mycobacterium produces toxin that kills cells • Mad cow – prion, spongiform encephalopathy, fatal
Conservation Medicine • Ecological diseases - animal epidemics • A viral hemorrhagic disease, Great Lakes fish; ballast. • California sea lions have herpes 1 virus spread from human sewage. • Sudden Oak Death (fungus) oak, redwoods, and Douglas fir trees in California. • Dermo, protozoan parasite destroying oyster beds and spreading along the east coast due to climate warming. • Conservation medicine – examines how environmental changes threaten the health of humans and natural communities
Pesticide Resistance • Natural selection and the ability of organisms to evolve rapidly • Human tendencies to overuse pesticides speeds up this process. • The protozoan parasite that causes malaria is now resistant to most antibiotics, while the mosquitoes that transmit it have developed resistance to many insecticides.
Antibiotic Resistance • 50% of the 100 million antibiotic doses prescribed in the U.S. every year are unnecessary or are the wrong drug. • Many people do not finish the full-course, creating resistant strains of bacteria. • ie. Antibiotic resistant strains of MRSA are spreading through hospitals in the US and China resulting in thousands of deaths. • Antibiotics are routinely fed to U.S. farm animals to stimulate weight gain. These are excreted in urine and feces, and find their way into surface waters where they create more antibiotic resistance.
Funding Health Care • Heaviest burden of illness borne by poorest people who cannot afford a healthy environment or adequate health care. • Increased financial aid to developing countries could reduce the spread of pathogens and might stabilize population growth since parents whose children have a higher survival rate tend to have fewer offspring.
Funding Health Care • WHO estimates 90% of all disease burden occurs in developing countries where less than 10% of all health care dollars are spent. • Millions of people are dying of treatable infections and parasitic diseases. • 2% of people with AIDS have access to modern medicines. • 600,000 infants acquire HIV every year through mother-to-child transmission during birth or breast feeding.
Toxicology • Toxicology is the study of poisons and their effects on living systems. • Toxins • are poisons. • React with cellular chemicals and disrupt metabolic functions. Some of their damage can be irreversible. • Are dangerous even in very small amounts, e.g. on trillionth of a gram.
Toxicology • Dangerous chemicals are divided into two broad categories: • Toxic - poisonous • Can be general or very specific. Often harmful even in dilute concentrations. • Hazardous - dangerous • Flammable, explosive, irritant, acid, caustic
Ecotoxicology • Ecotoxicology - the interactions, transformation, fate, and effects of natural and synthetic chemicals in the biosphere. • Chronic wasting disease, CWD, is spreading in deer and elk in North America. It is caused by a prion, a protein that belongs to the family of the mad-cow disease and Creutzfelt-Jacob disease in humans. • Domoicacid is produced by a marine phytoplankton. DA is nerve toxin that kills marine mammals and birds. Algal outbreaks have been caused by agricultural fertilizers washed to the sea.
Classes of Toxins • Allergens • Immune System Depressants • Endocrine Disrupters • Neurotoxins • Mutagens • Teratogens • Carcinogens
Toxins • Allergens - substances that activate the immune system causing hypersensitivity • Antigens - substances that are recognized as foreign by white blood cells and stimulate the production of specific antibodies • Other allergens act indirectly by binding to other materials so they become antigenic. • Sick Building Syndrome due to formaldehyde sensitivity
Toxins 2. Immune System Depressants - pollutants that depress the immune system increasing susceptibility to opportunistic infections (pesticides) • PCBs • Benzene • Dyes • Heavy metals • Asbestos
Toxins 3. Endocrine Disrupters - synthetic chemicals that block, mimic or interfere with hormones, the chemical messengers that control how an organism develops and functions • Related effects: interrupted sexual development; thyroid system disorders; inability to breed; reduced immune response; abnormal mating and parenting behavior. • Environmental estrogens - environmental contaminants which cause reproductive problems in animals even at very low doses • Dioxin and dioxin-like compounds, polychlorinated biphenyls, DDT and other pesticides, plasticizers such as bisphenol A
Toxins 4. Neurotoxins - metabolic poisons that specifically attack nerve cells • Different types act in different ways. • Heavy Metals kill nerve cells. • Anesthetics and Chlorinated Hydrocarbons disrupt nerve cell membranes. • Organophosphates and Carbamatesinhibit signal transmission between nerve cells.
Toxins 5. Mutagens - Agents that damage or alter genetic material. Can lead to birth defects or tumors. • Polycyclic aromatic hydrocarbon (PAH) 6. Teratogens - specifically cause abnormalities during embryonic growth and development • Alcohol - Fetal Alcohol Syndrome 7. Carcinogens - substances that cause cancer • Cancer is the 2nd leading cause of death. • 1 in 2 males and 1 in 3 females in the U.S. will have cancer in their lifetime.
Diet • Correlation between a high fat/high salt diet and cardiovascular disease • Fruits, vegetables, whole grains, complex carbohydrates, and fiber are beneficial. • Sixty-percent of all U.S. adults are now considered overweight due to over nutrition. • U.S. Centers for Disease Control warn one in three U.S. children are at risk of becoming diabetic.
Diet • Certain groups of people live up to 120 + years old. • These groups have in common... • Clean air and water. • Little stress due to uniform and predictable life. • Dry and sunny climate at middle altitudes. • Active and vigorous life in non-industrialized setting. • All ages work together for the benefit of the community. • The elderly are respected. • Family shares in work, religion and recreation. • Low fat diet, rich in fiber and vegetables and fruits.
Movement, Distribution, and Fate of Toxins • How chemicals move through the ecosystem depends on: • chemical composition • solubility • stability • reactivity • Availability of a vehicle such a solvent to carry the toxic agent is important. • Toxicity is determined by the stability and how a toxin is stored in the environment.
Movement, Distribution, and Fate of Toxins • Solubility - one of most important characteristics in determining the movement of a toxin • Chemicals are divided into two major groups: • Water soluble compounds move rapidly through the environment and have access to cells. • Fat soluble compounds need a carrier to move through the environment. Fat-soluble molecules penetrate tissues and accumulate in lipid deposits where they will not be degraded by metabolic reactions and persist for many years.
Rachel Carson - A Voice for Nature • In 1962, Silent Spring alerted the public to the dangers of indiscriminate pesticide use. • Carson called for selective, ecologically sound use of pesticides. • All 12 of the most toxic agents in her book were banned or severely restricted.
Peregrine falcons disappeared from the eastern U.S. in 1960s due to excess pesticide use
“DDT (dichlorodiphenyltrichloroethane) Powerful Insecticide, Harmless to Humans” 45
Pesticides and Child Development in Mexico’s Yaqui Valley • Elizabeth Guillette (anthropologist) – 1994 • Valley farmers used pesticides but foothill farmers continued traditional farming • Valley children were far behind foothill children developmentally in: • Coordination • Physical endurance • Long-term memory • Fine-motor skills (Less exposure to pesticides) (More exposure to pesticides) (Brennan & Withgott 2005)
Exposure and Susceptibility • Airborne toxins generally cause more ill health than any other exposure. • Lining of lungs easily absorbs toxins. • Food, water and skin contact are other ways to be exposed to toxins. • Largest toxin exposure reported in industrial settings • Time of the exposure and health of the organism have strong influence on toxicity. Children more vulnerable than adults.
Bioaccumulation and Biomagnification • Cells can selectively absorb and accumulate certain chemicals. • This is called bioaccumulation. e.g. nutrients, minerals. • Toxins can also accumulate in body tissues and reach dangerous levels. • Biomagnification - occurs when there is an increase in concentration of certain substances in successive higher trophic levels of the food chain. • Example: DDT